MIKHEYEV, AS; University of Texas at Austin: Patterns of herbivory in leaf-cutting ants (Atta cephalotes)

Leaf cutting ants are dominant herbivores of neotropical forests harvesting 12-17% of the leaves around their nests and possessing remarkable dietary breadth. In contrast with other studies, which assumed that leaf cutter foraging is guided by interspecific vairability in plant palatability, I propose that all trees have an equal size-dependent probability of containing a palatable patch. This model predicts the well documented greater harvest of relatively larger trees. When fitted to field data, the two-parameter model explained 92% of the variation in the number of trees harvested between colonies. Additionally, the model predicts the species composition of the diet should parallel that of the surrounding community, a pattern again seen in the field data. Additionally, I evaluate the statistical foraging model in light of two other hypotheses that have been proposed to explain aspects of leaf cutter ant foraging: (a) the preference for pioneer tree species and (b) an optimal foraging model. I found no evidence for either hypothesis in my data set. By ignoring species differences in palatability and treating food sources in the vicinity of the colony as a whole, the statistical foraging model may provide a bridge between the ecosystem and ant foraging behavior.